Piezo electric crystal apparatus



NOVO 8;; 1932. HUND 1,886,814

PIEZO ELECTRIC CRYSTAL APPARATUS Original Filed Feb. 26, 1926 fllozmu nm LU Patented Nov. 8, 1932 UNITED STATES PATENT OFFICE AUGUST HUNI), OF

WIRED RADIO,

IBETHESDA, MARYLAND, ASSIGNOB, BY MESNE ASSIGNMENTS, TO

INCL, OF NEW YORK, N. Y., A CORPORATION OF DELAWARE PIEZO ELECTRICCRYSTAL APPARATUS August 16, 1927.

My invention relates broadly to piezo electric apparatus and moreparticularly to a system for selectively adjusting the frequency ofpiezo electric oscillators by crystal means.

This application is a division of my application Serial No. 90,934,filed February 26, 1926.

One of the objects of my invention is to provide a system for accuratelyadjusting the frequency of a piezo electric oscillator system forsecuring a desired frequency independent of the grinding depth of thepiezo electric crystal used in the oscillator.

Another object of my invention is to provide a piezo electric crystalapparatus having means for selectively varying the capacity relationshipbetween the piezo electric crystal used in the generation ofoscillations of constant frequency and the conductive plate whichestablishes electrical connection between one surface of the crystal andthe external electric circuit whereby the frequency developed by thecrystal may be shifted to a selected condition in order to accuratelyadjust the oscillating circuit with which the crystal is associated.

Still another object of my invention is to provide means for shiftingthe frequency generated by a piezo electric crystal by slight amounts inorder to secure a desired frequency independent of the grinding of thecrystal.

Still another object of my invention is to provide a piezo electriccrystal apparatus wherein a piezo electric crystal is provided withmeans for subjecting the crystal to mechanical. forces for shifting thefrequency at which the crystal may be operated in an electrical circuitto a desired value independent of the grinding of the crystal at itsfundamental frequency.

A further object of my invention is to provide a piezo electric crystalapparatus where a piezo electric crystal is used in the generation ofoscillations having means for selectively loading the piezo electriccrystal by light weights of different values for changing the frequencyat which the crystal operates in an oscillation circuit to a desired alNo. 90,934. Divided and this application filed Serial No. 213,407.

value independent of the grinding of the crystal.

A still further object of my invention is to provide means for varyingthe frequency at which a piezo electric crystal will operate in anelectrical circuit by means of variations in pressure upon the surfaceof the piezo electric crystal by the positive introduction of forcesagainst one surface of the crystal tending to a desired value withoutthe necessity of regrinding the crystal for the desired frequency.

Other and further objects of my invention will be understood from thespecification hereinafter following by reference to the accompanyingdrawing, wherein:

Figure 1 represents diagrammatically a piezo electric crystal apparatusembodying the principles of my invention; Fig. 2 1s a detail view of apiezo electric crystal apparatus showing an adjustable contact platewhich is provided with respect to the upper surface of the crystal forvarying the frequency at which the crystal will sustain oscillations inan electron tube circuit; Fig. 3 is a modified view of a piezo electriccrystal in which an upper contact plate may be va ried in spacialrelation with respect to the upper surface of a piezo electric crystaland actually subjected to pressure against the upper surface of thepiezo electric crystal for shifting the frequency of operation to adesired degree; and Fig. 4 shows a modified piezo electric crystalapparatus construction where the upper surface of the piezo electriccrystal may be loaded by small weights for selecting a desired frequencyof operation independent of the grinding depth of the crystal.

In my copending application Serial No. 59,677, filed September 30, 1925,I have described a method of accurately cutting piezo electric plates toa size by which a frequency of predetermined characteristics will begenerated. Certain laws have been developed by which the frequency atwhich piezo electric crystal plates when out according to my processwill be established. Having once ground a piezo electric plate for thegeneration of a to shift the frequency of oscillation given frequencyhowever, it is necessary to sustain oscillations of that frequency alonein an electron tube oscillator circuit and the operation of the circuitis constant at the selected frequency. In order to secure oscil lationsof any other frequency it is necessary to regrind the piezo electricplate and thus present an entirely different piezo electric plate in theinput circuit of the oscillator. By my present invention I provide meanswhereby the frequency of a piezo electric crystal oscillator may beshifted to a desired value by the introduction of mechanical forces;with respect to the crystal or the variations in capacity relationshipbetween one of the electrodes establishing connection with the piezoelectric crystal and the upper surface of the piezo electric crystal. Bya slight variation in spacial relation between one electrode and onesurface of the piezo electric crystal I am enabled to shift thefrequency which will be sustained by the piezo electric crystal in anelectron tube oscillator circuit independent of the grinding of thecrystal. I have also discovered that by subjecting the piezo electriccrystal to mechanical strain by the introduction of positive pressureagainst the crystal that the frequency of operation may be shifted to adesired degree. In the piezo electric crystal apparatus of my inventionI provide means for selecting the pressure to which the piezo electriccrystal is subjected to an extremely fine degree. The pressure must beregulated within a range of very definite limits and the spacialrelation between the electrodes and the surface of the crystal must bevery accurately adjusted in order to secure a desired shift in thefrequency.

Referring to the drawing in more detail, reference character 1represents an electron tube arranged in an oscillator circuit which ispiezo electric crystal controlled. The electron tube includes filamentelectrodela, grid electrode 16 and plate electrode 10. The filamentelectrode 1a isheated from battery 2 through rheostat 3. An oscillationcircuit 4 is arranged in the output circuit of the electron tube andincludes an adjustable tuning condenser 5 and variable inductance 6. Theplate circuit of the oscillator includes high potential battery 7 andobserving meter 8 and telephone headset 9. A by-pass condenser 10 isshunted across the elements 7, 8 and 9 facilitating the setting up ofoscillations in the circuit. The piezo electric crystal which controlsthe oscillator circuit is shown at 11 resting on contact plate 12 andhaving a variably related contact plate 14. The contact plate 14 can bemoved toward or away from the piezo electric crystal 11 and occupiesselected positions spacially related to the piezo electric crystal asrepresented by the dotted line 15. The movable contact plate 14 connectsto a switch arm 17 as represented at 16. The switch arm 17 is arrangedto be moved to contact '18 or 19 for connecting the piezo electriccrystal across the input circuit or across the grid and plate electrodesof the oscillator.

One form which the piezo electric apparatus may assume is illustratedmore clearly in Fig. 2 where the movable electrode or contacting plate14: is carried by a screw 21 adjustable in threads'20 by means ofadjusting knob 22, By this arrangement the upper con tact plate 14 maybe moved toward or away from the upper surface of piezo electric crystalll for varying the spacial relation and the capacity relationship withrespect to the piezo electric crystal for selecting an operatingfrequency of a desired value inde-' pendent of the initial grinding ofthe crystal. In F 1g. 3 I have shown a method of varying the spacialrelationship between the upper plate 1 land the upper surfaceof thepiezo electric crystal 11 and actually impressinga mechanical force onthesurface of the piezo electric crystal for shifting the frequency to adesired degree. In this construction a lever 24 is pivotally mounted at25 and at the end furthest from the fulcrum a spring 26 is attached andsecured to the plate member 27 of the adjustable screw 28. Theadjustable screw 28 may be advanced or retracted in screw threads 29 bymeans of knob 30 for varying the spacial relationship between plate 1iand the upper surface of the crystal 11. A special link connection isprovided between the contact plate 14 and the lever 24 as has beenrepresented by the vertically extending linl: 28. The contact plate 14by reason of this link connection always occupies a horizontal positionwith respect to the upper surface of the piezo electric crystal so thatitis advanced or retracted withrespect to the upper surface of the piezoelectric crystal always in parallel planes. Pressure may be placed uponthe surface of the piezo electric crystal as determined by thecompression under which spring 26 is placed.

In Fig. 4 I have shown a construction wherein a lever 31, pivoted at 33in notch 32 of the lever, is variably weighted near one end 3 lforvarying the pressure upon the upper surface of the piezo electriccrystal 11 or varying the spacial relationship between the electrodesand the upper surface of the piezo electric crystal 11. The weight35.may be moved along the scale 3-1 for determining the pressure uponthe upper surface of the piezo electric crystal for the desired shift infrequency from the fundamental frequency of the crystal. I find thatusually onethird of one millimeter is a proper size of gap for thedesired shift in frequency. The gap may be varied, however, between onemillimeter to a slight pressure against the upper surface of By a slightpreswhich the upper the piezo electric crystal. sure, I mean a conditionin contact plate touches the piezo electric plate and can be forcedthereagainst in order to secure a desired tension in the piezo electriccrystal for adjusting the frequency thereof to a desired degree.

In short wave generators where the regrinding of thin piezo electricdisks is dillicult, the slight variation in frequency which isobtainable by a variation in spacial relation between the contact plateand the surface of the piezo electric crystal is very desirable. VJhereactual pressure is placed ipon the piezo el ctric crystal, the shift infrequency is more marked than with the mere variation in spacialrelation between the upper electrodes and the upper surface of therystal. In circuits where two piezo electric crystal oscillators areemployed in the production of audio frequency current, the slight shiftin frequency which is possible by means of the methods described herein,provides a method for varying the pitch of the audio frequency notewithout change in the constants of the circuits of the oscillators.

it will be understood that many other applications of the var ation infrequency of the piezo electric cr tal oscillator may be readilysuggested from the principles set forth herein and I intend nolimitations upon my invention other than are imposed by the scope of theappended claims.

h at I claim as new and desire to secure by Letters Patent of the UnitedStates is as follows:

1. Piece electric crystal apparatus comprising in combination a piezoelectric plate, a pair of flat conductive members for supporting saidpiezo electric plate, and means for subjecting said plate to pressure orreleasing qressure therefrom for shifting the operating frequencythereof, said means comprising a lever member pivotally mounted adjacentsaid flat conductive members.

2. PieZo electric crystal apparatus comprising in combination a piezoelectric plate, a metallic electrode for supporting said piezo electricplate and establishing electrical connection with one face of said piezoelectric plate, a lever member pivotally mounted adjacent said metallicelectrode, a second metallic electrode carried by said lever member andadjustable with respect to the opposite face of said piezo electricplate for establishing connection therewith at a frequency dif ferentthan the fundamental frequency of said crystal.

3. Piezo electric crystal apparatus comprising in combination a piezoelectric plate, a metallic electrode for supporting said piezo electricplate and establishing electrical connection with one face of said piezoelectric plate, a lever member pivotally mounted adjacent said metallicelectrode, a second metallie electrode carried by said lever member andadjustable with respect to the opposite face of said piezo electricplate, and spring means acting through said lever for varying thepressure of said second electrode upon said piezo electric plate.

4. The method of varying the responsive frequency of a piezo electriccrystal oscillator which comprises subjecting the crystal oscillator toelectrode pressure.

5. The method of selectively adjusting the frequency of a piezo electriccrystal oscillator which consists in selectively applying electrodepressure to said crystal oscillator.

6. In a piezo electric crystal oscillator system the method of shiftingthe frequency of the crystal oscillator which consists in subjecting thecrystal to variable pressure for selectively sustaining a desiredfrequency.

7 Piezo electric crystal apparatus com prising, in combination, a piezoelectric element having opposed faces, an electrically conductive memberin intimate contact with one face of said element, a second electricallyconductive member disposed in parallel relation to the opposite face ofsaid piezo electric element and movable into and out of contacttherewith, and resilient means for varying the pressure between saidsecond electrically conductive member and said piezo electric elementwhen in contact therewith while maintaining the parallel relationtherebetween.

8. A piezo electric crystal, electrodes for said crystal and means forselectively adjusting to a desired value the vibrating frequency of saidcrystal comprising resilient means for varying the pressure exerted onsaid crystal by said electrodes.

In testimony whereof I affix my signature.

AUGUST HUND.

